The present invention relates to hermetic seals for sealed devices and, more particularly, hermetic seals around electrical feedthrough pins.
Implantable medical devices having external leads or other electrical connections require feedthroughs that extend from the inside of the medical device to the outside. The feedthrough may be shaped as a cylindrical pin and have connectors on either end. The implantable device needs to be protected from the influx of external gases or liquids present in the body. Such influx of gases and/or liquids into the medical device may cause the device to malfunction. Therefore, the implantable medical device is typically hermetically sealed. The feedthrough exit points on the medical device housing, however, are points where the hermetic seal can be broken.
The connector pin or the feedthrough are generally made from non-corrosive metals including, but not limited to, titanium, platinum, platinum alloys such as platinum/iridium, and stainless steels.
The surrounding insulating material around the metal feedthrough, however, is typically made of glass or ceramic. Because of the difference in the thermal coefficient of expansion (“TCE”) between the metal feedthrough and glass or ceramic insulator, a gap can develop between the feedthrough and the insulating glass or ceramic, thereby breaking the hermetic seal.
One method for preventing this break in the hermetic seal is to coat the metal feedthrough pin with an oxidation layer over the surface of the pin. This oxidation layer increases the adhesion between the pin surface and the insulating glass or ceramic and also increases the mean path length through the seal. Nevertheless, this method does not prevent the tendency to produce a gap between the metal pin and surrounding glass or ceramic insulation and moreover, inconsistent sealing can result because the method is fairly sensitive to manufacturing variations in the oxidation layer.
What is needed therefore is a feedthrough sealing design which positively reduces or eliminates gapping in the seal between the insulator and metal feedthrough pin.